It is hypothesized that adenoviral-mediated gene transfer of human OTC cDNA into liver of adults with partial OTC deficiency will be effective and safe in correcting the underlying metabolic disorder. In this Phase I FDA approved study, a dose response curve will be established to determine the dose to be used in a subsequent Phase II study that will include children. The aim of the Phase I study is to establish a dose that will achieve effective gene transfer without significant toxicity.